Under this legal doctrine, an attorney may not reveal the nature and subject of discussions between the client and him/herself. This includes (but is not limited to) face-to-face or telephone conversations, letters and emails. The theory behind this doctrine is that clients must be able to speak freely about their issues without the fear that some piece of information may be used against them.
When a trial, deposition or hearing is held, the attorney is legally obligated to refuse to answer any questions that may reveal any part of his or her contact with the client. The client may voluntarily choose to reveal such information, but has no legal obligation to do so. Any formal documents that have been prepared on behalf of the client also fall into this category.
Occasionally, just what constitutes attorney-client privilege is not entirely clear. For example, if a federal contractor is out drinking in a bar with a friend who just happens to be an attorney and brags about how he milked FEMA for a million five, then later an audit shows that goods and services were not provided, it is highly doubtful that either could claim attorney-client privilege.
On the other hand, if this contractor had come to his friend's office cold sober during regular business hours or had arranged a meeting specifically to discuss the issue, rules of attorney-client privilege would apply.
Unfortunately, situations of this nature are often difficult to prove one way or the other, and the inclination of the courts is to err on the side of caution.
The principles of attorney-client privilege also apply to the relationships between physician or mental health practitioner and patient as well as between clergy and parishioner.